The invention relates to a piston pump, which is particularly provided for a vehicle brake system.
Pump pistons of this kind are known in and of themselves. They have a piston that is contained so that the piston can move axially in a sleeve and can be driven into a reciprocating stroke motion. The sleeve is inserted into a cylinder bore of a pump housing, which can constitute a hydraulic block of the vehicle brake system. On an end remote from the piston drive, the cylinder bore is sealed in a pressure-tight manner in relation to the outside with a sealing part that is inserted into it.
In known piston pumps, a check valve is inserted into the sealing part as an outlet valve and cooperates with a valve seat at a bottom of the sleeve. An outflow from the piston pump takes place by means of radial outlet bores in the sealing part or also in the sleeve, which communicate with an outlet in the pump housing. Outlet bores of this kind in the sealing part or in the sleeve have the disadvantage that they must be produced in a cutting fashion in a separate work cycle. Moreover, letting a bore radially into a cylindrical part results in difficulties. The production of the outlet bores is therefore costly and time-consuming.
The piston pump according to the invention, has a through flow conduit as an inlet or outlet, which is constituted by a groove in a bottom of the sleeve and/or by a groove in the sealing part, which is covered by the sealing part or by the sleeve or its bottom so that the groove becomes a conduit. The through flow conduit can also be embodied jointly by a groove in the sleeve and a groove in the sealing part. The through flow conduit is thus disposed between the sealing part and the sleeve. The invention has the advantage that the sleeve and the sealing part, including the through flow conduit that constitutes the pump inlet or pump outlet, can be produced rapidly and inexpensively as formed parts in a non-cutting work cycle, in particular as cold-formed parts, for example by means of cold pressing.
Furthermore, a through flow conduit that is disposed a small distance from the valve seat in the axial direction of the piston pump, which is made possible by means of letting a groove into the sleeve or into the sealing part, courteracts the production of noise when flow passes through the check valve.
In order to reduce noise production when flow passes through the check valve, it is favorable if, starting from a center plane of a valve ball of the check valve, which plane will be called the equator below and simultaneously constitutes a radial plane of the piston pump, the through flow conduit feeds, offset in the direction of the valve seat, into a valve chamber that contains the valve ball. The offset of the mouth of the through flow conduit from the equator of the valve ball to the valve seat should be approx. 20-30% of a radius of the valve ball or more. In other words, viewed in the axial direction, the through flow conduit should lead from the valve chamber close to the valve seat. An explanation for the reduction in noise production is that when flow passes through the check valve, it does not completely circulate around the valve ball, wherein a complex circulation would develop, which would excite the valve ball to uncontrolled oscillating movements, but rather that after passing the valve seat, the flow is deflected directly to the side in the direction of the through flow conduit. As a result, only a small fraction of the surface of the valve ball is subjected to a flow; for the most part, the valve ball is surrounded by static fluid. The requirement to have the through flow conduit come out close to the valve seat can be realized particularly well through its embodiment as a groove, especially if the groove is let into a bottom of the sleeve.
Through the production of the through flow conduit by means of a groove, the through flow conduit can be embodied with no trouble as flat and wide and as a result, can likewise come close to the valve seat in the axial direction. However, this reaches a limit when the through flow resistance becomes too great at a given through flow cross section. A width of the through flow conduit of approx. 60 to 65% of the diameter of the valve ball is viewed as favorable, with a height of the through flow conduit that is approx. 20-30% of its width. Furthermore, the disposition of the mouth of the through flow conduit close to the valve seat has the advantage that the valve ball cannot close the through flow conduit when flow is passing through the check valve since it rests with its equator against a wall of the valve chamber on an end of the through flow conduit remote from the valve seat.
It furthermore aids in the reduction of noise production if only one through flow conduit leads from the valve chamber, since a flow through the valve is deflected exclusively in one direction, namely toward the single through flow conduit, by means of which the valve ball is deflected in the direction of the through flow conduit and rests against the end of the through flow conduit, against the wall of the valve chamber. As a result, an oscillation of the valve ball is prevented. The above-mentioned measures for preventing noise production can also be used with valve closing bodies that differ from the ball shape.
In order to keep the shaping forces low when manufacturing the grooves that constitute the through flow conduit, in one embodiment of the invention, the provision is made that a section of the through flow conduit leading from the valve chamber is let into the sleeve bottom and another, outward-leading part of the through flow conduit is let into the sealing part Since the sleeve is preferably comprised of steel and the sealing part is preferably comprised of an aluminum alloy, the shaping forces are reduced and it is nevertheless possible to dispose the valve-side mouth of the through flow conduit close to the valve seat.
An annular groove preferably in the sealing part, assures that the groove in the sleeve bottom communicates with the groove in the sealing part, independent of an angular position of the sealing part in relation to the sleeve. This obviates the need for measures which assure a rotationally fixed attachment of the sealing part with regard to the sleeve.
The piston pump is provided in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. The abbreviations ABS, ASR, FDR, or EHB are used for such brake systems, depending on the type of brake system. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to supply brake fluid out of a storage tank into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR, FDR, or EHB). The pump is required, for example, in a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (FDR) and/or an electrohydraulic brake system (EHB). With wheel slip control (ADS or ASR), for example, a locking of the wheels of the vehicle during a braking event when there is strong pressure on the brake pedal (ABS) and/or a spinning of the driven wheels of the vehicle when there is strong pressure on the gas pedal (ASR) can be prevented. In a brake system that serves as a steering aid (FDR), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump supplies the brake fluid into the wheel brake cylinder or cylinders if an electrical brake pedal sensor detects an actuation of the brake pedal or in which the pump is used to fill is a reservoir of the brake system.